Behavioural Brain Research;Volume 360, 15 March 2019
The energy deficit hypothesis of attention-deficit/hyperactivity disorder (ADHD) suggests that low lactate production by brain astrocytes causes the symptoms of the disorder. Astrocytes are the main producers of lactate in the brain; however, skeletal muscles can produce the most lactate in the body. The lactate production by skeletal muscles increases with physical activity, as does the expression of the lactate transporter monocarboxylate transporter 1 (MCT1) at the blood-brain barrier (BBB). We hypothesise that children with ADHD, by being hyperactive, increase lactate production by skeletal muscles and transport it into the brain to compensate for low supply by astrocytes. The aim of this study was to explore whether the level of MCT1 is altered in the brain in an animal model of ADHD. The MCT1 expression was quantified on hippocampal brain sections from the best available rat model of ADHD, i.e., the spontaneously hypertensive rat (SHR) (n=12), and the relevant control, the Wistar Kyoto rat (WKY) (n=12), by the use of quantitative immunofluorescence laser scanning microscopy and postembedding immunogold electron microscopy. The results revealed significantly higher levels of hippocampal MCT1 immunoreactivity in SHR compared to WKY, particularly at the BBB. These results indicate that lactate flux through MCT1 between the body and the brain could be upregulated in children with ADHD. This study adds to previous research suggesting hyperactivity may be beneficial in ADHD; Children with ADHD possibly display a hyperactive behaviour in order to raise skeletal muscle lactate production, MCT1 expression and flux over the BBB to supply the brain with lactate.